Non-rotary cutting tool and process of machining scroll member by using the same

ABSTRACT

A non-rotary cutting tool which is to be moved relative to a workpiece in a predetermined direction for cutting the workpiece, with its rake face being held substantially perpendicular to the predetermined direction. The cutting tool includes (a) a generally cylindrical shank portion, and (b) a generally semi-cylindrical body portion which has an outer circumferential surface constituted by the rake face and a semi-cylindrical surface. The semi-cylindrical body portion has a cutting edge which is defined by an edge of the rake face and which is covered with a diamond coating. Also disclosed is a process of machining a scroll member of a scroll compressor by using this non-rotary cutting tool.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates in general to a non-rotary cuttingtool, and more particularly to such a non-rotary cutting tool that canbe easily manufactured and used in a finishing step of a machiningprocess.

[0003] 2. Discussion of the Related Art

[0004] There is known a scroll compressor as one type of compressorwhich is used in a refrigeration or air conditioning system, forcompressing a gas used as a refrigerant in the system. The scrollcompressor is constructed to include a pair of scroll members which arearranged in an opposing manner with the scroll members beinginterfitted. The scroll members are given a relative orbiting motionwith respect to each other, so that each of successive series ofenclosed spaces defined by the scroll members progressively decreases involume as it moves inwardly from a radially outer position to a centralposition. With the decrease in the volume of the enclosed space, a fluidsuch as a gas introduced into the enclosed space is compressed and isthen discharged from the enclosed space.

[0005]FIG. 5A is a perspective view of a fixed scroll member 100 whichis to be fixed to a housing (not shown) of the scroll compressor, whileFIG. 5B is a perspective view of an orbiting scroll member 103 which isto be brought into meshing engagement with the fixed scroll member 100.The fixed scroll member 100 includes a base plate 101 and an involute orscroll wall 102 extending from the base plate 101 in a directionsubstantially perpendicular to the base plate 101. Similarly, theorbiting scroll member 103 includes a base plate 104 and an involute orscroll wall 105 extending from the base plate 104 in a directionsubstantially perpendicular to the base plate 104. In an operation ofthe scroll compressor, the orbiting scroll member 103 held in engagementwith the fixed scroll member 100 is rotated relative to the fixed scrollmember 100, as shown in FIG. 6, whereby the gas within each of theenclosed spaces is compressed and is then discharged from the enclosedspace through a discharge port 106 formed through the central positionof the base plate 101 of the fixed scroll member 100. In this instance,the compression efficiency is increased with an increase in degree offluid tightness between the scroll walls 103, 105. Therefore, in aprocess of machining the scroll members 100, 103, it is necessary thatthe scroll walls 103, 105 be machined with a high degree of accuracy. Ina conventional process of machining a scroll wall of a scroll member, asdisclosed in JP-A-H11-336657 (publication of unexamined Japanese PatentApplication laid open in 1999), its roughing, semi-finishing andfinishing steps are carried out by using rotary cutting tools such asend mills.

[0006] In the conventional machining process, however, each end millattached to a spindle of a machine tool through a holder tends to sufferfrom its “run out” while being rotated with the spindle. In a finishingstep of a machining process, the run out of the end mill makes itimpossible to obtain a sufficiently high degree of machining accuracy,which is required in machining of scroll walls of a scroll compressor,for assuring a sufficiently high degree of fluid tightness between thescroll walls and a sufficiently high degree of compression efficiency inthe scroll compressor. The degree of fluid tightness is inevitablyreduced with reduction in the accuracy of the machining of the scrollwalls, thereby problematically making it difficult to obtain thesufficiently high degree of compression efficiency in the scrollcompressor. Further, it is also difficult to obtain an end millinherently suitable for finishing the scroll walls which require to befinished with a considerably high machining accuracy.

SUMMARY OF THE INVENTION

[0007] The present invention was made in view of the background priorart discussed above. It is therefore a first object of the presentinvention to provide a non-rotary cutting tool which is easilymanufactured and is capable of exhibiting a high degree of machiningaccuracy required in a finishing step of a machining process. This firstobject may be achieved according to any one of first through eighthaspects-of the invention which are described below. It is a secondobject of the invention to provide a process of advantageously machininga scroll member of a scroll compressor, by using the non-rotary cuttingtool. This second object may be achieved according to either of ninthand tenth aspects of the invention which are described below.

[0008] The first aspect of this invention provides a non-rotary cuttingtool which is to be moved relative to a workpiece in a predetermineddirection for cutting the workpiece, with a rake face thereof being heldsubstantially perpendicular to the predetermined direction, the cuttingtool comprising: (a) a generally cylindrical shank portion; and (b) agenerally semi-cylindrical body portion which is coaxial with thecylindrical shank portion and which has an outer circumferential surfaceconstituted by the rake face and a semi-cylindrical surface, wherein thesemi-cylindrical body portion has a cutting edge which is provided by anedge of the rake face and which includes a covered portion covered witha diamond coating.

[0009] According to the second aspect of the invention, in thenon-rotary cutting tool defined in the first aspect of the invention,the cutting edge includes a side cutting edge portion and an end cuttingedge portion which are contiguous to each other, wherein the sidecutting edge portion is defined by an intersection of the rake face andthe semi-cylindrical surface, while the end cutting edge portion isdefined by an intersection of the rake face and an axially distal endface of the semi-cylindrical body portion, and wherein at least one ofthe side cutting edge portion and the end cutting edge portion of thecutting edge is covered by the diamond coating.

[0010] According to the third aspect of the invention, in the non-rotarycutting tool defined in the second aspect of the invention, the sidecutting edge portion and the end cutting edge portion of the cuttingedge intersect with each other at a corner which is so sharp that thecorner has a nose radius of not larger than 0.05 mm.

[0011] According to the fourth aspect of the invention, in thenon-rotary cutting tool defined in any one of the first through thirdaspects of the invention, the diamond coating has a surface abraded orsmoothed to have a surface roughness Rz of not larger than 1.60 μm.

[0012] According to the fifth aspect of the invention, in the non-rotarycutting tool defined in any one of the first through fourth aspects ofthe invention, at least one of the side cutting edge portion and the endcutting edge portion of the cutting edge is so sharp that a radius oneach of the above-described at least one of the cutting edge portion andthe end cutting edge portion is not larger than 0.03 mm.

[0013] According to the sixth aspect of the invention, in the non-rotarycutting tool defined in the second or third aspect of the invention, theside cutting edge portion of the cutting edge has a high degree ofparallelism with respect to an axis of the cylindrical shank portionsuch that an error in the parallelism is not larger than 3 μm, whereinthe end cutting edge portion of the cutting edge has a high degree ofperpendicularity with respect to the axis of the cylindrical shankportion such that an error in the perpendicularity is not larger than 3μm.

[0014] According to the seventh aspect of the invention, in thenon-rotary cutting tool defined in any one of the first through sixthaspects of the invention, wherein the cylindrical shank portion and thesemi-cylindrical body portion are provided by a single piece.

[0015] According to the eighth aspect of the invention, in thenon-rotary cutting tool defined in any one of the first through seventhaspects of the invention, the rake face is provided by a flat surfacewhich is elongated in an axial direction of the semi-cylindrical bodyportion and which has a width smaller than a diameter of the cylindricalshank portion.

[0016] The ninth aspect of this invention provides a process ofmachining a scroll member of a scroll compressor which has a base plateand a scroll wall extending from the base plate in a directionsubstantially perpendicular to the base plate, by using a non-rotarycutting tool comprising (a) a generally cylindrical shank portion, and(b) a generally semi-cylindrical body portion which is coaxial with thecylindrical shank portion and which has an outer circumferential surfaceconstituted by a rake face and a semi-cylindrical surface, wherein thesemi-cylindrical body portion has a cutting edge which is defined by anedge of the rake face and which is covered with a diamond coating, theprocess comprising a step of moving at least one of the non-rotarycutting tool and the scroll member relative to the other in such adirection that permits the scroll wall and the base plate to be machinedby the cutting edge, while holding the rake face substantiallyperpendicular to the direction.

[0017] According to the tenth aspect of the invention, in the methoddefined in the ninth aspect of the invention, the cutting edge includesa side cutting edge portion and an end cutting edge portion which arecontiguous to each other, wherein the scroll wall and the base plate aremachined by the side cutting edge portion and the end cutting edgeportion of the cutting edge, respectively.

[0018] The non-rotary cutting tool defined in any one of the firstthrough eighth aspects of the invention is advantageously used formachining a slot or groove in a workpiece. In the machining operation,at least one of the cutting tool and the scroll member is moved relativeto the other or each other in a predetermined direction, while the rakeface of the cutting tool is held substantially perpendicular to thepredetermined direction. Since the cutting tool is not rotated in themachining operation, the machined workpiece is free from deteriorationin its accuracy which could be caused by “run out” of the cutting tool.Where this non-rotary cutting tool is used for machining a pair ofscroll members of a scroll compressor, as in the ninth aspect of theinvention, the pair of scroll members can be machined with a higherdegree of accuracy than where it is machined by a rotary cutting toolsuch as an end mill which is likely to suffer from its run out, so thatit is possible to obtain a higher degree of fluid tightness betweenscroll walls of the respective scroll members and accordingly a higherdegree of compression efficiency in the scroll compressor.

[0019] In the process of machining each scroll member of the scrollcompressor, the machining process can be completed by implementations ofonly two steps, i.e., a roughing step and a finishing step which may becarried out with an end mill and the present non-rotary cutting tool,respectively. This is advantageous over the conventional process ofmachining the scroll member with end mills, which requiresimplementation of three steps, i.e., a roughing step, a semi-finishingstep and a finishing step. That is, the machining process with use ofthe present non-rotary cutting tool eliminates necessity of theimplementation of the semi-finishing step, thereby advantageouslyleading to an increased efficiency of manufacturing of the scrollcompressor with a reduced cost.

[0020] Further, the present non-rotary cutting tool capable of finishingthe scroll member of the scroll compressor with a high degree ofmachining accuracy is easier to manufacture, than an end mill which isto be used in the finishing step of the conventional process ofmachining the scroll member.

[0021] Further, owing to the diamond coating covering the entirety orpart of the cutting edge, the cutting edge is prevented from beingundesirably deflected in the machining operation.

[0022] In the non-rotary cutting tool defined in the third aspect of theinvention, the corner at which the side cutting edge portion and the endcutting edge portion intersect with each other is so sharp that the noseradius of the corner is 0.05 mm or less. Where this non-rotary cuttingtool is used for machining a pair of scroll members of a scrollcompressor, such a small nose radius of the corner permits a cornerbetween the scroll wall and the base plate of each scroll member (whichare respectively machined by the side cutting edge portion and the endcutting edge portion of the cutting edge) to have a small radius ofcurvature. The small radius of curvature of the corner between thescroll wall and the base plate leads to a high degree of fluid tightnessbetween the scroll walls of the pair of scroll members, when they areheld in engagement with each other, so that the compression efficiencyof the scroll compressor is increased.

[0023] In the non-rotary cutting tool defined in the fourth aspect ofthe invention, the diamond coating has a surface abraded or smoothed tohave the surface roughness with maximum height Rz of not larger than1.60 μm. Such a high degree of smoothness of the surface of the diamondcoating is effective to provide the workpiece with a high degree ofsurface smoothness in the finishing step of the machining process.

[0024] In the non-rotary cutting tool defined in the fifth aspect of theinvention, a chamfer or radius on at least one of the side cutting edgeportion and the end cutting edge portion of the cutting edge is notlarger than 0.03 mm. Such a sharp cutting edge facilitates machining ofthe workpiece with a sufficiently high degree of accuracy in thefinishing step of the machining process.

[0025] In the non-rotary cutting tool defined in the sixth aspect of theinvention, the side cutting edge portion of the cutting edge has thehigh degree of parallelism with respect to the axis of the cylindricalshank portion such that the error in the parallelism is not larger than3 μm, while the end cutting edge portion of the cutting edge has thehigh degree of perpendicularity with respect the axis of the cylindricalshank portion such that the error in the perpendicularity is not largerthan 3 μm. In other words, the side cutting edge portion is notdeviated, by an amount larger than 3 μm, from a geometrical straightline which is precisely parallel with the axis of the cylindrical shankportion, while the end cutting edge portion is not deviated, by anamount larger than 3 μm, from a geometrical straight line which isprecisely perpendicular to the axis of the cylindrical shank portion.Such a minimum error in the contour of the cutting tool is advantageous,especially, where the cutting tool is used for finishing a workpiece,such as the scroll member of the scroll compressor, which requires to befinished with a high degree of machining accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, features, advantages and technicaland industrial significance of this invention will be better understoodby reading the following detailed description of the presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings, in which:

[0027]FIG. 1 is a set of three views of a non-rotary cutting tool whichis constructed according to a first embodiment of the invention, whereina front view, a side view and a bottom view of the cutting tool aregiven at (a), (b) and (c), respectively;

[0028]FIG. 2 is a table indicating specifications of the non-rotarycutting tool and an end mill used in a cutting test, and cuttingconditions in the cutting test;

[0029]FIG. 3 is a table indicating a result of the cutting test;

[0030]FIG. 4A is a front view of a non-rotary cutting tool which isconstructed according to a second embodiment of the invention;

[0031]FIG. 4B is a front view of a non-rotary cutting tool which isconstructed according to a third embodiment of the invention;

[0032]FIG. 5A is a perspective view of a fixed scroll member as aproduct machined by the non-rotary cutting tool of the invention;

[0033]FIG. 5B is a perspective view of an orbiting scroll member as aproduct machined by the non-rotary cutting tool of the invention;

[0034]FIG. 6 is a set of views showing an operation of a scrollcompressor which is constituted by the fixed scroll member and theorbiting scroll member; and

[0035]FIG. 7 is a view illustrating a machining operation in which thescroll member of the scroll compressor is machined by the non-rotarycutting tool of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] Referring first to FIG. 1, there will be described a non-rotarycutting tool 1 which is constructed according to a first embodiment ofthe invention. FIG. 1 is a set of three views of the non-rotary cuttingtool 1, wherein its front view, side view and bottom view are given at(a), (b) and (c), respectively. The non-rotary cutting tool 1 is aso-called “gooseneck tool”, and is to be held at its end portion (rightend portion as seen at (a), (b) of FIG. 1) by a suitable tool holder(not shown) so that the cutting tool 1 is fixed to a spindle of amachine tool (not shown) such as a machining center through the suitabletool holder. This non-rotary cutting tool 1 is advantageously used, forexample, in a finishing step of a process of machining a scrollcompressor, as shown in FIG. 7.

[0037] The non-rotary cutting tool 1 is provided by a substrate (singlepiece) formed of a cemented carbide which is made from, for example,tungsten carbide (WC) in a powder-metallurgy process includingcompacting and sintering steps. The cutting tool 1 includes a generallysemi-cylindrical body portion 2 which has a generally semi-circularcross sectional shape (as shown at (c) of FIG. 1), and a generallycylindrical shank portion 3 which is coaxially contiguous to a proximalend portion of the semi-cylindrical body portion 2 (i.e., right endportion of the body portion 2 as seen at (a), (b) of FIG. 1). Thecutting tool 1 is held at the shank portion 3 by the tool holder, sothat the cutting tool 1 is attached to a machine tool through the toolholder.

[0038] The semi-cylindrical body portion 2, serving as a cutting bladeportion, has a rake face 8 consisting of a flat surface which liessubstantially on an axis of the cylindrical shank portion 3, and acutting edge 4 which is defined by an edge of the rake face 8. Thesemi-cylindrical body portion 2 has an outer circumferential surfaceconstituted by the rake face 8 and a semi-cylindrical surface. The rakeface 8, provided by the flat surface, is elongated in an axial directionof the semi-cylindrical body portion 2, and has a width smaller than adiameter of the cylindrical shank portion 3. The cutting edge 4 includesa side cutting edge portion 5 located at each of widthwise opposite endsof the rake face 8, and an end cutting edge portion 6 located at anaxially distal end of the rake face 8. In other words, the side cuttingedge portion 5 is provided by an intersection of the rake face 8 and thesemi-cylindrical surface, while the end cutting edge portion 6 isprovided by an intersection of the rake face 8 and an axially distal endface of the semi-cylindrical body portion 2. The side cutting edgeportion 5 and the end cutting edge portion 6 intersect substantiallyperpendicularly with each other, as shown at (a) of FIG. 1. A nose orcorner at which the side and end cutting edge portions 5, 6 intersectwith each other is so sharp to have a nose radius of not larger than0.05 mm.

[0039] The semi-cylindrical body portion 2 is coated at its surface witha diamond coating in accordance with CVD method, so that the cuttingedge 4 including the side and end cutting edge portions 5, 6 is coveredwith the diamond coating. In the present embodiment, the diamond coatinghas a thickness of about 6-20 μm. The diamond coating is likely toeasily peel off the body portion 2 if its thickness is smaller than 6μm. The thickness of larger than 20 μm is not appropriate from aneconomical point of view.

[0040] The diamond coating is ground by a grindstone such that thesurface of the diamond coating is smoothed to have a roughness withmaximum height Rz of not larger than 1.60 μm. It is noted that thediamond coating may be otherwise smoothed, for example, by means oflaser, ion-beam, thermochemical-mechanical polishing ormechanical-chemical polishing.

[0041] A portion of the semi-cylindrical surface immediately below theside cutting edge portion 5 is ground so as to serve as a side flankface, such that a side-relief angle α between this side flank face and aline drawn through the side cutting edge portion 5 perpendicularly tothe rake face 8 is 5°, as shown at (a) of FIG. 1. The side cutting edgeportion 5 is so sharp that a chamfer or radius on the side cutting edgeportion 5 is not larger than 0.03 mm. Further, the side cutting edgeportion 5 is not deviated, by an amount larger than 3 μm, from ageometrical straight line which is precisely parallel with the axis ofthe cylindrical shank portion 3. In other words, the side cutting edgeportion 5 has a high degree of parallelism with respect to the axis ofthe cylindrical shank portion 3 such that an error in the parallelism isnot larger than 3 μm.

[0042] An end-relief angle β between an end flank face (provided by theaxially distal end face of the semi-cylindrical body portion 2) and aline drawn through the end cutting edge portion 6 perpendicularly to therake face 8 is 5°, as shown at (b) of FIG. 1. The end cutting edgeportion 6 is so sharp that a chamfer or radius on the end cutting edgeportion 6 is not larger than 0.03 mm. Further, the end cutting edgeportion 6 is not deviated, by an amount larger than 3 μm, from ageometrical straight line which is precisely perpendicular to the axisof the cylindrical shank portion 3. In other words, the end cutting edgeportion 6 has a high degree of perpendicularity with respect to the axisof the cylindrical shank portion 3 such that an error in theperpendicularity is not larger than 3 μm.

[0043] In a machining operation with the non-rotary cutting tool 1constructed as described above, the cutting tool 1 is moved relative toa workpiece in a predetermined direction, while being kept unrotated andmaintaining such a posture that permits the rake face 8 to be heldsubstantially perpendicular to the predetermined direction, so that theworkpiece is cut by the side and end cutting edge portions 5, 6 of thecutting edge 4. FIG. 7 is a view illustrating a machining operation inwhich the scroll member of the scroll compressor is machined by thenon-rotary cutting tool 1. In this machining operation performed in amachining center equipped with a rotary table that is rotatable about Aaxis, the scroll member mounted on the rotary table is controlled to bemoved relative to the cutting tool 1 (attached to a spindle of themachining center) in at least one of X-axis and Y-axis directions at apredetermined feed rate, while being rotated about A axis at apredetermined angular velocity, so that the scroll wall 105 and the baseplate 104 are machined by the side cutting edge portion 5 and the endcutting edge portion 6 of the cutting edge 4, respectively.

[0044] Referring next to tables of FIGS. 2 and 3, there will bedescribed a result of a test which was conducted for verifying technicaladvantages of the non-rotary cutting tool 1 constructed as describedabove. In this test, a workpiece in the form of the scroll member of thescroll compressor as shown in FIGS. 5A and 5B is machined by the cuttingtool 1 and also by an end mill, for comparing machining accuracyprovided by the cutting tool 1 with that provided by the end mill.

[0045] The table of FIG. 2 indicates specifications of the cutting tool1 and the end mill, and cutting conditions in the test. The “SURFACEROUGHNESS” in the cutting tool 1 means a surface roughness at the sideand end cutting edge portions 5, 6 of the cutting edge 4, while that inthe end mill means a surface roughness at its peripheral and end cuttingedges. The “NOSE RADIUS” in the cutting tool 1 means a nose radius ofthe corner at which the side and end cutting edge portions 5, 6intersect with each other, while that in the end mill means a noseradius of a corner at which the peripheral and end cutting edgesintersect with each other. The “PERPENDICULARITY” in the cutting tool 1means an error in perpendicularity of the end cutting edge portion 6with respect to the axis of the cylindrical shank portion 3, while thatin the end mill means an error in perpendicularity of the end cuttingedge with respect to the axis of its cylindrical shank portion. The“RADIUS ON CUTTING EDGE” in the cutting tool 1 means a chamfer or radiuson each of the side and end cutting edge portions 5, 6, while that inthe end mill means a chamfer or radius on each of the peripheral and endcutting edges.

[0046] The table of FIG. 3 indicates the result of the cutting test. The“ROUGHNESS OF MACHINED SURFACE” means a roughness of the surfacemachined by each of the cutting tool 1 and the end mill. The “RADIUS OFCURVATURE” means a radius of the curvature on a corner between thescroll wall and the base plate in the scroll member machined by each ofthe cutting tool 1 and the end mill. The “PERPENDICULARITY” means aperpendicularity of the scroll wall with respect to the base plate inthe scroll member machined by each of the cutting tool 1 and the endmill.

[0047] As apparent from the table of FIG. 3, the non-rotary cutting tool1 of the invention exhibited a better performance, than the end mill, inall of the smoothness of the machined surface, the sharpness on thecorner between the scroll wall and the base plate, and theperpendicularity of the scroll wall with respect to the base plate. Inthe machining with the non-rotary cutting tool 1, the accuracy ofcontour of the cutting edge 4 was precisely reflected in the accuracy ofthe machined workpiece. On the other hand, in the machining with the endmill, the accuracy of contour of the end mill was not preciselyreflected in the accuracy of the machined workpiece. Describedspecifically, the radius of the curvature on the corner in the scrollmember was 0.05 mm which was larger than the nose radius in the end mill(=0.03 mm). The perpendicularity in the scroll member was 4.9 μm whichwas larger than the perpendicularity in the end mill (=2 μm). It isconsidered that the deterioration in the accuracy of the workpiecemachined by the end mill was due to undesirable run-out and deflectionof the end mill during the machining operation.

[0048] As described above, in the non-rotary cutting tool 1, owing tothe hard diamond coating, the cutting edge portions 5, 6 covered by thediamond coating are given a high degree of rigidity so as to beprevented from being deflected in the machining operation. Further, thesurface of the diamond coating is ground to have a high degree ofsurface smoothness that is effective to provide the workpiece with ahigh degree of surface smoothness in the finishing step of the machiningprocess.

[0049] Where the non-rotary cutting tool 1 is used for machining each ofthe scroll members 100, 103 of the scroll compressor, at least one ofthe cutting tool 1 and the scroll member is moved relative to the otheror each other in a predetermined direction, while the rake face 8 of thecutting tool 1 is held substantially perpendicular to the predetermineddirection, so that the scroll wall and the base plate are machined bythe side and end cutting edge portions 5, 6, respectively. Since thecutting tool 1 is not rotated in the machining operation, the machinedscroll member is free from deterioration in its accuracy which could becaused by “run out” of the cutting tool. That is, the pair of scrollmembers 100, 103 can be machined with a higher degree of accuracy thanwhere it is machined by a rotary cutting tool such as an end mill whichis likely to suffer from its run out, so that it is possible to obtain ahigher degree of fluid tightness between scroll walls 102, 105 of therespective scroll members 100, 103 and accordingly a higher degree ofcompression efficiency in the scroll compressor.

[0050] Since the non-rotary cutting tool 1 is capable of machining eachscroll member with a high machining accuracy, a finishing step of theprocess of machining each scroll member can be carried out by thiscutting tool 1. It is noted that a roughing step of the machiningprocess may be carried out by a conventional end mill.

[0051] Further, the present non-rotary cutting tool 1 capable offinishing the scroll member of the scroll compressor with a high degreeof machining accuracy is easier to manufacture, than an end mill whichis to be used in the finishing step of the conventional process ofmachining the scroll member.

[0052] Further, in the non-rotary cutting tool 1, the corner at whichthe side and end cutting edge portions 5, 6 intersect with each other isso sharp that the nose radius of the corner is 0.05 mm or less. Wherethe non-rotary cutting tool 1 is used for finishing the pair of scrollmembers 100, 103 of the scroll compressor, since the corner between thescroll wall and the base plate is given substantially the same shape asthe sharp corner between the side and end cutting edge portions 5, 6, itis possible to obtain a high degree of fluid tightness between thescroll walls 102, 105 of the pair of scroll members 100, 103, when theyare held in engagement with each other, so that the compressionefficiency of the scroll compressor is increased.

[0053] Further, in the non-rotary cutting tool 1, the diamond coatinghas a surface ground or smoothed to have the surface roughness withmaximum height Rz of not larger than 1.60 μm. Such a high degree ofsmoothness of the surface of the diamond coating is effective to providethe workpiece with a high degree of surface smoothness in the finishingstep of the machining process.

[0054] Further, in the non-rotary cutting tool 1, the chamfer or radiuson each of the side cutting edge portion 5 and the end cutting edgeportion 6 of the cutting edge 4 is not larger than 0.03 mm. Such a sharpcutting edge facilitates machining of the workpiece with a sufficientlyhigh degree of accuracy in the finishing step of the machining process.

[0055] Further, in the non-rotary cutting tool 1, the error in theparallelism of the side cutting edge portion 5 with respect to the axisof the cylindrical shank portion 3 is not larger than 3 μm, while theerror in the perpendicularity of the end cutting edge portion 6 withrespect to the axis of the cylindrical shank portion 3 is not largerthan 3 μm. Such a minimum error in the contour of the cutting tool 1 isadvantageous, especially, where the cutting tool 1 is used for finishinga workpiece, such as the scroll member of the scroll compressor, whichrequires to be finished with a dimensional error within a considerablysmall amount of tolerance.

[0056] Referring next to FIG. 4A, there will be described a non-rotarycutting tool 20 which is constructed according to a second embodiment ofthe invention. The same reference numerals as used in the cutting tool 1of the first embodiment will be used to identify the elements which arethe same as those in the cutting tool 1. No redundant description ofthese elements will be provided.

[0057]FIG. 4A is a front view showing in enlargement itssemi-cylindrical body portion 22 of the non-rotary cutting tool 20. Thiscutting tool 20 is identical with the cutting tool 1 of the firstembodiment of the invention, except for its cutting edge 24, morespecifically, the shape of its end cutting edge portion 26. That is,while the end cutting edge portion 6 of the cutting tool 1 is providedby a straight linear edge, the end cutting edge portion 26 of thiscutting tool 20 is provided by a substantially arcuate-shaped edge whichis convexed in a direction away from the cylindrical shank portion 3(not shown), i.e., in the upward direction as seen in FIG. 4A. The endcutting edge portion 26 as well as the side cutting edge portion 5 iscovered by a diamond coating which is ground to have a smoothed surface,as in the cutting tool 1.

[0058] This non-rotary cutting tool 20 provides substantially the sametechnical advantage as the non-rotary cutting tool 1 of the firstembodiment, and is capable of forming, in a workpiece, a slot or groovehaving a smoothly curved bottom surface. In a process of manufacturingthe cutting tool 20, the body portion 22 may be formed to have apredetermined contour corresponding to a cross sectional shape of theslot or groove that is to be formed with the cutting tool 20. After theformation of the body portion 22 with the predetermined contour, thecutting edge 24 is coated with the diamond coating, and the diamondcoating is then ground. Thus, the body portion 22 is easily given thepredetermined contour.

[0059] Referring next to FIG. 4B, there will be described a non-rotarycutting tool 30 which is constructed according to a third embodiment ofthe invention. The same reference numerals as used in the cutting tool 1of the first embodiment will be used to identify the elements which arethe same as those in the cutting tool 1.

[0060]FIG. 4B is a front view showing in enlargement itssemi-cylindrical body portion 32 of the non-rotary cutting tool 30. Thiscutting tool 30 is identical with the cutting tool 1 of the firstembodiment of the invention, except for its cutting edge 34, morespecifically, the shape of its end cutting edge portion 36. That is,while the end cutting edge portion 6 of the cutting tool 1 is providedby a straight linear edge perpendicular to the axis of the cylindricalshank portion 3, the end cutting edge portion 36 of this cutting tool 30is provided by a substantially V-shaped edge which is convexed in adirection away from the cylindrical shank portion 3 (not shown), i.e.,in the upward direction as seen in FIG. 4B. The end cutting edge portion36 as well as the side cutting edge portion 5 is covered by a diamondcoating which is ground to have a smoothed surface, as in the cuttingtool 1.

[0061] This non-rotary cutting tool 30 provides substantially the sametechnical advantage as the non-rotary cutting tool 1 of the firstembodiment, and is capable of forming, in a workpiece, a slot or groovehaving a substantially V-shaped cross section. In a process ofmanufacturing the cutting tool 30, the body portion 32 may be formed tohave a predetermined contour corresponding to a cross sectional shape ofthe slot or groove that is to be formed with the cutting tool 30. Afterthe formation of the body portion 32 with the predetermined contour, thecutting edge 34 is coated with the diamond coating, and the diamondcoating is then ground. Thus, the body portion 22 is easily given thepredetermined contour.

[0062] While some embodiments of the present invention have beendescribed above in detail for illustrative purpose only, it is to beunderstood that the invention is not limited to the above-describedembodiments but may be otherwise embodied.

[0063] For example, the side cutting edge portion 5 of the cutting edge4 may be provided at each of the widthwise opposite ends of the rakeface 8, or alternately, may be provided at a selected one of thewidthwise opposite ends of the rake face 8.

[0064] Although there has not been described that in the abovedescription, it is possible to recycle or reutilize the above-describedcutting tools 1, 20, 30. That is, when the diamond coating covering thecutting edge or the cutting edge per se is damaged or worn as a resultof long-time service of the cutting tool, the substrate of the cuttingtool can be recycled or reutilized, instead of preparing a newsubstrate. For example, the cutting tool having the worn coating may beburnt in a furnace, so that the worn coating is burned out or removedfrom the substrate. The substrate is recoated with the diamond coating,and the substrate recoated with the diamond coating is then ground so asto have a resharpened cutting edge. Thus, the recycle or reutilizationof the cutting tools can be easily made, leading to a reducedmanufacturing cost.

[0065] It is to be understood that the present invention may be embodiedwith various other changes, modifications and improvements, which mayoccur to those skilled in the art, without departing from the sprit andscope of the invention defined in the following claims:

What is claimed is:
 1. A non-rotary cutting tool which is to be moved relative to a workpiece in a predetermined direction for cutting the workpiece, with a rake face thereof being held substantially perpendicular to said predetermined direction, said cutting tool comprising: a generally cylindrical shank portion; and a generally semi-cylindrical body portion which is coaxial with said cylindrical shank portion and which has an outer circumferential surface constituted by said rake face and a semi-cylindrical surface, wherein said semi-cylindrical body portion has a cutting edge which is provided by an edge of said rake face and which is covered with a diamond coating.
 2. A non-rotary cutting tool according to claim 1, wherein said cutting edge includes a side cutting edge portion and an end cutting edge portion which are contiguous to each other, wherein said side cutting edge portion is defined by an intersection of said rake face and said semi-cylindrical surface, while said end cutting edge portion is defined by an intersection of said rake face and an axially distal end face of said semi-cylindrical body portion, and wherein at least one of said side cutting edge portion and said end cutting edge portion of said cutting edge is covered by said diamond coating.
 3. A non-rotary cutting tool according to claim 2, wherein said side cutting edge portion and said end cutting edge portion of said cutting edge intersect with each other at a corner which is so sharp that said corner has a nose radius of curvature of not larger than 0.05 mm.
 4. A non-rotary cutting tool according to claim 1, wherein said diamond coating has a surface smoothed to have a surface roughness Rz of not larger than 1.60 μm.
 5. A non-rotary cutting tool according to claim 2, wherein at least one of said side cutting edge portion and said end cutting edge portion of said cutting edge is so sharp that a radius on each of said at least one of said side cutting edge portion and said end cutting edge portion is not larger than 0.03 mm.
 6. A non-rotary cutting tool according to claim 2, wherein said side cutting edge portion of said cutting edge has a high degree of parallelism with respect to an axis of said cylindrical shank portion such that an error in said parallelism is not larger than 3 μm, and wherein said end cutting edge portion of said cutting edge has a high degree of perpendicularity with respect to said axis of said cylindrical shank portion such that an error in said perpendicularity is not larger than 3 μm.
 7. A non-rotary cutting tool according to claim 1, wherein said cylindrical shank portion and said semi-cylindrical body portion are provided by a single piece.
 8. A non-rotary cutting tool according to claim 1, wherein said rake face is provided by a flat surface which is elongated in an axial direction of said semi-cylindrical body portion and which has a width smaller than a diameter of said cylindrical shank portion.
 9. A process of machining a scroll member of a scroll compressor which has a base plate and a scroll wall extending from the base plate in a direction substantially perpendicular to the base plate, by using a non-rotary cutting tool comprising (a) a generally cylindrical shank portion, and (b) a generally semi-cylindrical body portion which is coaxial with said cylindrical shank portion and which has an outer circumferential surface constituted by a rake face and a semi-cylindrical surface, wherein said semi-cylindrical body portion has a cutting edge which is defined by an edge of said rake face and which is covered with a diamond coating, said process comprising: a step of moving at least one of said non-rotary cutting tool and said scroll member relative to the other in such a direction that permits the scroll wall and the base plate to be machined by said cutting edge, while holding said rake face substantially perpendicular to said direction.
 10. A process according to claim 9, wherein said cutting edge includes a side cutting edge portion and an end cutting edge portion which are contiguous to each other, and wherein the scroll wall and the base plate are machined by said side cutting edge portion and said end cutting edge portion of said cutting edge, respectively. 